M13 bacteriophage-activated superparamagnetic beads for affinity separation

The growth of the biopharmaceutical industry has created a demand for new technologies for the purification of genetically engineered proteins. The efficiency of large-scale, highgradient magnetic fishing could be improved if magnetic particles offering higher binding capacity and magnetization were available. This article describes several strategies for synthesizing SPMs that are composed of a M13 bacteriophage layer assembled on a superparamagnetic core. Chemically cross-linking the pVIII proteins to a carboxyl functionalized SPM produced highly responsive superparamagnetic particles with a side-on oriented, adherent virus monolayer. Also, the genetic manipulation of the pIII proteins with a His6 peptide sequence allowed reversible assembly of the bacteriophage on a nitrilotriacetic acid functionalized core in an end-on configuration. These phage-magnetic particles were successfully used to separate antibodies from high-protein concentration solutions in a single step with a > 90 % purity. The dense magnetic core of these particles makes them five times more responsive to magnetic fields than commercial materials composed of polymer-iron oxide composites and a monolayer of phage could produced a 1000 fold higher antibody binding capacity. These new bionanomaterials appear to be well-suited to large-scale highgradient magnetic fishing separation and promise to be cost effective as a result of the selfassembling and self-replicating properties of genetically engineered M13 bacteriophage.